Activation of the latissimus dorsi (lats) during back exercises is something a lot of people struggle with. One of the reasons for this is that you can't actually see your back during these exercises, this makes the mind muscle connection more difficult. Also, trying to lift too much weight forcing correct form to collapse is a big factor.

Some things to keep in mind when performing back exercises.

1) Hold your core nice and tight with a slight arch in your back the whole movement to prevent injury and maintain strict form. Taking a breath in and holding it at the start of the movement will assist with this.
2) Always choose correct form over total weight lifted. Using sloppy form may allow you to use more weight, which some might think leads to more overload. This is incorrect because that extra weight isn't being moved by your lats. How do we know this? Because if your lats were able to move that weight, you would be able to use it with strict form.
3) When performing Lat pull-down, keep your head up and your chest out. Keep your elbows back nice and tight, focus on squeezing your shoulder blades together and you will correct this common problem.
4) For all back exercises rather than thinking you are pulling with your hands imagine they are merely hooks, focus on pulling from your elbows and rear deltoid. 
5) The lats on average have an equal amount of slow and fast twitch muscle fibers, so they respond best to medium volume. 
6) The traps are a postural muscle and are predominantly slow twitch so they will respond better to greater volume. Traps are important, train them properly and train them more than your chest.
7) Its easy to think that training a 1:1 ratio of push to pull will achieve structural balance but this is not quite correct, for optimal result you should have a greater pull volume than push. 

Keeping all this in mind when training back will stimulate much greater hypertrophy (growth) and will ensure you're getting the best results for your efforts. Train smart.